This invention concerns an improved process for preparing alkanol and vicinal glycol ester compounds, including ester derivatives of ethylene glycol, by reaction of oxides of carbon with hydrogen.
In copending, commonly assigned application Ser. No. 968,655, filed Dec. 11, 1978, now abandoned, the inventive process concerns the selective co-synthesis of alkanol and glycol esters, particularly the ester derivative of ethylene glycol, methanol and ethanol, by the catalytic reaction of carbon monoxide and hydrogen in the presence of a liquid medium containing a carboxylic acid co-reactant. Catalysis is effected in the presence of a catalyst containing osmium or ruthenium transition metals, in combination with specific classes of co-catalyst salt species. The process is exemplified by, but not limited to, the one step co-synthesis of ethylene glycol diacetate, methyl acetate and ethyl acetate from carbon monoxide, hydrogen mixtures--commonly known as synthesis gas--in the presence of an acetic acid (HOAc) liquid medium according to the stoichiometry of eqs. (1) to (3): ##STR1##
Methyl acetate, ethyl acetate and glycol diacetate are all products of recognized commercial value, particularly as chemical intermediates and extractive solvents. Methyl and ethyl acetates are used widely as solvents, primarily for surface coatings. Ethylene glycol diacetate is useful in the production of ethylene glycol, an important component in polyester fiber and antifreeze formulations. Free glycol may be generated from its diacetate derivative via hydrolysis, as disclosed, for example, in Belgium Pat. No. 749,685.
It is the purpose of this invention and that of the just mentioned companion case to provide new routes to the preparation of alkanol and diol esters using mixtures of carbon monoxide and hydrogen (commonly called synthesis gas or syngas) as the primary building block. This is particularly true where methyl acetate, ethyl acetate and glycol diacetate are the principal products (eqs. 1-3), since in this case acetic acid is the co-reactant media, and one route to HOAc manufacture is from synthesis gas via methanol carbonylation. ("Trends in Petrochemical Technology" by A. M. Brownstein, Chapter 5 (1976)).
In recent years, a large number of patents have been issued dealing with the synthesis of lower molecular weight hydrocarbons, olefins, alkanols etc. from synthesis gas. Of particular note, U.S. Pat. No. 2,636,046, discloses the synthesis of polyhydric alcohols and their derivatives by reaction between carbon monoxide and hydrogen at elevated pressures (&gt;1500 atm of 22,000 psi) and temperatures to 400.degree. C. using certain cobalt-containing catalysts. More recently, in Belgium Pat. No. 793,086 and U.S. Pat. No. 3,940,432 there is described the co-synthesis of methanol and ethylene glycol from mixtures of carbon monoxide and hydrogen using a rhodium complex catalyst. Typically, CO-hydrogenation is effected at 8000 psi of 1:1 H.sub.2 /CO synthesis gas, at 220.degree. C., using tetraglyme as the solvent, and dicarbonylacetylacetonatorhodium(I) in combination with an organic Lewis base as the catalyst precursor. (For summary of the work, see: R. L. Pruett, Annals New York Academy of Sciences, Vol. 295 p. 239 (1977)). While other metals of Group VIII of the Periodic Table have been tested for activity under similar conditions, including cobalt, ruthenium, copper, manganese, iridium and platinum, only cobalt was found to have slight activity. The use of ruthenium compounds in particular failed to produce polyfunctional products such as ethylene glycol. This is illustrated in U.S. Pat. No. 3,833,634 for solutions of triruthenium dodecacarbonyl.